Since sound is a shockwave with air molecules oscillating in longitudinal motion, I'm wondering what is the scenario when they just started to oscillate. While the amplitude might gradually increase to a certain limit, does it also mean speed of the wave will also gradually increase?
[Physics] Does a sound wave have to accelerate to get to that speed in air
acousticswaves
Best Answer
Sound isn't a thing that moves. Air moves. When we say a sound wave moves, what we mean is the place where air is moving changes. Air does accelerate. But the sound wave does not.
To generate a pulse of sound, you push the air next to you away and then move back to your original position. Typically you do this very quickly. For a low pitch, you might do this in $0.01$ second.
This doesn't really create wind. It creates a small region right next to you where air molecules have been pushed away, leaving fewer molecules than normal. Pressure is low here. Slightly farther away, there is a region where the molecules have been pushed. They are squeezed closer together than normal. The pressure is high here.
The molecules in the high pressure region push themselves apart. This fills in the low pressure region, and creates a high pressure region a little farther away.
The process keeps going. The place where there is high pressure keeps getting farther away at a constant speed. In regions ahead of it and behind it, air is at rest. In the high pressure region, air is accelerating and decelerating.